Typically, a tungsten silicide film is used combining with a polysilicon film, i.e. so called polycide structure, to reduce the resistance of the device. However, because the tungsten silicide film has high reflectivity (about 50% i-line) or the surface of the wafer has bad topography, the resolution of the photolithography is limited. Moreover, it results in uneven linewidth and a notching phenomena. In order to solve the phenomena, an anti-reflective coating layer is required to form on the tungsten silicide layer to decrease the reflectivity of the tungsten silicide layer. The anti-reflective coating layer can be a thin polysilicon layer (amorphous silicon), a titanium nitride layer, or an oxynitride layer (Si.sub.3 N.sub.4 O.sub.x). Another method for solving the phenomena is that an oxide layer is formed on the tungsten silicide layer by using chemical vapor deposition before the photolithography process starts. The oxide layer with the patterned photoresist serves as a hard mask to enhance the function of etching mask when etching the wafer to form the polycide structure.
The two aforementioned methods are to increase the resolution of linewidth in the wafer, whether forming a thin polysilicon layer (amorphous silicon), a titanium nitride layer, or an oxynitride layer (Si.sub.3 N.sub.4 O.sub.x) as an anti-reflective coating layer or an oxide layer as a hard mask. Unfortunately, the two conventional methods also increase the complexity of the process and burden in the production line so as to increase the cost of the product.